I have the same problem with my BSP I got a couple days ago, which is especially frustrating, because I like the workflow of the machine very much.
my setup: Live 8, Win7 64bit, BSP connected to PC via USB, Dark Energy II via CV, MFB 503 via MIDI out of the BSP. Audio Interface is Focusrite Saffire Pro 14 (firewire).
BSP is updated to the latest firmware.
it happens always after maybe half an hour. live actually doesn't crash, but the beatstep "freezes" with a stuttering loop sound. then I press stop on the BSP and it stops, but won't start again. if I try to unselect sync in the Ableton MIDI preferences, then Live freezes until I disconnect the beatstep. the only way to get it working again so far is to restart both the BSP and Live.
I haven't tried it yet to connect the Beatstep via DIN MIDI cable with the audio interface, but even if it works, I can't use the MIDI out of the interface for other stuff anymore, which is not a good solution.
please help me because I really don't want to return this thing, because otherwise it is a pretty awesome device! :/